1 Field of the Invention
The present invention relates to a lighting device, and particularly, to a lighting device that a serial/parallel connection structure of a light emitting device is changeable according to an input voltage.
2 Description of the Related Art
A light emitting diode (LED) refers to a kind of semiconductor device capable of realizing a light of various colors by configuring a light emitting source through forming a PN diode from a compound semiconductor. Such a light emitting device is advantageous in that it has a long life, miniaturization and weight-lightening are enabled, and low voltage driving is possible. In addition, such a light emitting device is robust to a shock and vibration, and warm-up time and complex driving are not necessary. The light emitting device may be applied to a backlight unit or various lighting devices by being mounted on a substrate or a lead frame in various types, packaged, and then modularized according to various uses
A plurality of LEDs are used to provide one independent lighting device, and at this point, the LEDs may be used with being connected serially or in parallel. At this point, in order for all the LEDs to be an ‘ON’ state all the time, commercial power is converted into DC power and then applied to the LEDs.
In this way, when DC power is supplied and used, an additional DC rectifying unit is necessary. However, a configuration of this DC rectifying unit may be removed and AC power may be directly applied to the LEDs. At this point, the LEDs may be connected serially and an ON/OFF state of each of the LEDs may be changed according to a magnitude of a varying input voltage. As the ON/OFF state is repeated, a flicker phenomenon occurs, a utilization rate of each of the LEDs becomes lowered, and accordingly light output efficiency is reduced.